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Comment by labcomputer | Hacker News Reader

Because then the distance between earth's pole and equator would no longer be 10,000 km.

Exactly. The definition of the meter was originally derived from the circumference of the Earth and the second is (now) defined as a specific number of vibrations of a particular state of a particular atom. If you want to change the meter to make the speed of light in vacuum a nice round number then you'll end up affecting pretty much all of the derived units upsetting the whole SI system.

And in the end it doesn't matter. You should just use the right number, which is arbitrary and landed on 7500 m/second and change short of being 'perfect' but it would have been an incredible coincidence if it did.

The reason that didn't happen is because the speed of light was one of the harder numbers to pin down and the first estimates and later refinements happened much later than the definition of the meter. And to complete the circle: the meter is now defined as a fraction of the speed of light! This has the interesting property that even though we may get better measurements for various constants the fixed ratio means that SI as a whole remains standing.

Thank you for the thorough explanation but I was thinking we could redefine the second.

That would also break SI in pretty terrible ways. So we're stuck with some numbers that don't look pretty in base 10, but if that bothers you can look at all natural constants in hex going forward and then they'd all be equally ugly.

What physics constants look like is for the most part a consequence of a number of accidents of history:

- the fact that apes have five fingers on each hand

- the fact that we have two hands

- the order in which the various constants were discovered

- some of the base items used for early definitions (which made complete sense at the time)

All of these to some extent factor in to that odd feeling that things are not as elegant as they could be.

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